Acoustic well logging involves placement of acoustic transducers (both for transmitters and receivers) in a sonde. The transducers are used to form vibratory energy waves which travel in the borehole and the formations adjacent to the sonde and to receive the returned waves. The vibratory energy waves are characterized as compression waves, shear waves, and pseudo-Rayleigh waves. In a transducer system which is axially symmetric, and in which the shear wave velocity is greater than borehole fluid velocity, the acoustic pulse at a receiver includes all three types of waves. In that situation, a full wave acoustic log can be obtained from the formation. However, there are formations in which the shear wave velocity is less than the borehole fluid velocity. In that instance, the transducers will not create the shear and pseudo-Rayleigh waves in conjunction with a radially symmetric pressure pulse.
According to theoretical developments, a nonaxially symmetric source would preferentially generate shear waves over compression waves. This then would enable acoustic logging techniques which involve shear wave analysis. In the past, the provision of transducers which preferentially form and respond to both kinds of waves (compression and shear) have not been available. Rather, duplicate sets of transducers for both the transmitter and receiver systems in acoustic logging devices have been used. Thus, one separate system would create and respond to the compression wave while a second system would create and respond to the shear wave. The apparatus of this invention sets forth a single transducer system that can be used to form both compression and shear wave pulses. Moreover, the system can be used for both transmission and receiving.